The purpose is to evaluate the immune response to viruses in healthy individuals and to identify abnormalities in these responses which may be related to the disease mechanisms. These sudies focus on functional analysis of the cellular immune response to viruses which commonly affect humans and in particular measles virus. The mechanisms involved in the regulation of these responses are being examined. An additional goal of these studies is to evaluate the influence of genetic makeup on both induction and effector phases of the immune response to viruses. Assays for cytotoxic T-cells, amplifier T-cells and suppressor T-cells directed at viruses are being developed. Virus antigens recognized by these cell populations and the influence of antigen presentation on the generation of these responses are being examined. Finally, these investigations apply findings obtained in healthy individuals to the evaluation of patients with the diseases of the nervous system, particularly multiple sclerosis which may involve immunological or infectious mechanisms. Longitudinal studies of both normal individuals and patients will be conducted.